1. Field of the Invention
The present invention relates to pulsed, electric discharge initiated gas lasers and more particularly to a parallel plate condensor/transmission line discharging across a very high volume of the gas in the laser cavity.
2. Description of the Prior Art
Laser action in certain of the rare gas halides has in the prior art been effected by electron beam excitation. This form of excitation however has self-imposed limitations on the pulse repetition rate. This rate is limited by heating of the electron beam exit window in the wall of the generator vacuum chamber and the lack of availability of high repetition rate switching for control of the electron beam. Other pulsed gas lasers have been successfully operated by the use of high output power, electric discharge energization. One of the more promising configurations providing the electric discharge is a parallel-plate driven pulsed nitrogen laser described by Levatter and Lin, Applied Physics Letters, Vol. 25, No. 12 (Dec. 15, 1974). The configuration of their device is basically a modified form of the Blumlein-type traveling wave discharge device utilizing parallel-plate transmission lines.
The Blumlein-type discharge device employes a pair of coplanar conductor sheets with linear spaced apart confronting edges constituting the anode and cathode of the discharge device with the lasing gas occupying the volume in the gap between the electrodes. The discharge energy is thus directly applied to and absorbed by gas. At one side or face of the coplanar conductor plates is a coextensive grounded plate separated from the conductors by a dielectric. The conductor plates and grounded plate thus form two capacitors allowing the buildup of a high charge in each conductor plate. The grounding of one conductor plate creates a high potential differential across the gap between the electrodes resulting in a discharge across the gap.
The achievement of ideal electrical characteristics in the Blumlein-type parallel-plate transmission line/capacitor arrangement requires that the capacitor elements be firmly pressed together uniformly over their entire surface areas with the sheet of dielectric sandwiched therebetween. Lack of uniformity in the capacitor sandwich results in spot potential variations between the plates and the minimum inductance of the plates in their function as transmission lines will not be attained. Massive mechanical clamps have been used to compress the capacitor elements with some degree of success. These however are cumbersome and their assembly and disassembly involve undue effort and time. In addition, the life span of the construction is shortened as a result of corona discharge at the edges of the plates thus generating ozone, which in turn erodes the dielectric.
Even with the advantages afforded by the Levatter and Lin electric discharge apparatus, and other known systems, the lasing gas volume is limited, thereby limiting pulse power. Also, even with best available operating parameters in the electric discharge and electron beam excitation systems, lasing has not been achieved in certain rare gas-halide media, such as krypton fluoride. The controlling parameters are the rise time to peak power of the discharge in the laser cavity and uniform discharge without arcing at high pressure. The rise time to peak charge on the parallel plate condensor is additionally significant since this factor, along with the discharge time elements, govern the maximum achievable laser pulse rate.
Another laser employing the Blumlein-type discharge is discussed by Basting et al, "A Simple, High Power Nitrogen Laser", Optoelectronics 4 (1972) 43-44.